Hand-held power tools, such as cordless screwdrivers, cordless drills or cordless impact drills have a high amount of drive torque. Limiting this torque is desirable for many applications. Adjustable torque limitation makes it possible, e.g., to screw a number of screws into a work piece with the same level of screw-down torque; a torque-limiting unit disengages as soon as the screws apply a certain level of torque resistance to the motor output shaft. The operator can adjust the torque-limiting unit according to the maximum torque required for the task at hand. A hand-held power tool with torque limitation of the type described above is made known in DE 103 09 057 A1.
Another hand-held power tool with a torque limiting unit is described in U.S. Pat. No. 7,455,123, and is fully incorporated in its entirety by reference. As described therein, the torque limiting unit has springs 26, 28 of different spring characteristics, i.e., using different spring rates, widths, lengths and/or stiffness. Requiring such different springs is costly as it is necessary to maintain a full inventory of different springs. It also makes assembly of the power tool difficult, as the assembler has to ensure each spring has been installed correctly in each place. Therefore, the likelihood of manufacturing defects is increased.
Accordingly, it is an object of the present invention to provide a hand-held power tool with a torque-limiting unit, which is a further improvement of the existing hand-held power tools.